Expandable polymeric composition

ABSTRACT

A POLYMERIC COMPOSITION COMPOSED OF A POLYMERIC THERMOPLASTIC MATERIAL AND 0.01-20% BY WEIGHT OF A UREA DERIVATIVE OF THE FORMULA:   R1-O-CH2-NH-CO-NH-R2   WHEREIN R1 IS HYDROGEN OR ALKYL OF 1-5 CARBON ATOMS AND R2 IS HYDROGEN OR -CH2OR1. THE UREA DERIVATIVE UNDERGOES CONDENSATION WITH THE SEPARATION OF WATER AND SIMPLE ALCOHOLS AND FUNCTIONS AS A CHEMICAL BLOWING AGENT AT AN ELEVATED TEMPERATURE WITHIN THE RANGE OF 100 TO 270* C.

United States Patent O 3,798,188 EXPANDABLE POLYMERIC COMPOSITION MakotoTakizawa, Ageo, Kinzo Miyamoto, Mitaka, Matahiko Asahi, Tokyo, andMegumu Nakamoto, Yokohama, Japan, assignors to Mitsui Toatsu Chemicals,Incorporated, Tokyo, Japan No Drawing. Filed Oct. 12, 1971, Ser. No.188,453 Int. Cl. C08j N20 US. Cl. 260-25 R 8 Claims ABSTRACT OF THEDISCLOSURE A polymeric composition composed of a polymeric thermoplasticmaterial and 0.0l20% by weight of a urea derivative of the formula:

wherein R is hydrogen or alkyl of l-S carbon atoms and R is hydrogen or-CH OR The urea derivative undergoes condensation with the separation ofwater and simple alcohols and functions as a chemical blowing agent atan elevated temperature within the range of 100 to 270 C.

BACKGROUND OF THE INVENTION This invention relates to an expandablepolymeric composition employing a novel blowing agent and to a processfor the production of shaped articles of cellular polymer therefrom.

In the production of shaped articles, the use of a blowing agent isknown to afford shaped articles of a cellular polymer. Known hitherto assuch blowing agent are low boiling compounds which vaporize during theshaping of polymers whereby cells are formed (physical blowing agents)and compounds which, under the influence of heat during the shaping ofpolymers evolve gases, so causing the formation of numerous cells(chemical blowing agents).

The physical blowing agent absorbes latent heat of vaporization onevaporation to gas to permit depression of the interfacial temperatureof the resulting cells. Thus, the use of the physical blowing agentimproves stability of foams and permits the production of highly foamedarticles of an expansion of more than 2, sometimes in excess of 3.However, the physical blowing agents are generally liquid having a highvapor pressure and tends to evaporate after mixed with a polymer. Inaddition, the majority of them is inflammable so that there is a dangerof fire in the use of them.

On the other hand, azo compounds are known as the chemical blowing agentwhich are generally solid and free from defects as seen in the physicalblowing agents but they decompose exothermally, so elevating thetemperature of the thermoplastic material along with evolving gases suchas N and CO. Thus, the use of such exothermic chemical blowing agentstends to impair the stability of foam cells and makes it difficult toproduce highly foamed articles of an expansion of more than 2, contraryto the case of physical blowing agents.

Details of the chemical blowing agents are described, for example, inManual for Foaming and Shaping Plastics, pp. 149-l54 published by theTechnological Association of Synthetic Resins, Japan (Tokyo). The amountof gas evolved is usually 100-280 ml./g. in terms of (volumetric amountof gas evolved at 0 C., 1 atm. in ml.)/ (weight of chemical blowingagent in g.).

The expansion referred to herein indicates (density of polymers)/(apparent density of shaped article of the polymer), the article ofexpansion of more than 2, being called highly foamed and that ofexpansion of 1.1-2 being called low foamed.

A method for preventing the formation of sink mark and hollow portionsin a polyolefin molded article caused by shrinkage, which comprisesadding a small amount (0.02-l% by weight) of a chemical blowing agent tothe polyolefin to form some fine cellular structure in the interior ofthe shaped article is taught in Japanese patent publn. No. 26,289/64.The expansion in this case is less than 1.1. When a known chemicalblowing agent is used for this method, small dimples are formed on thesurface of the shaped article, thus damaging appearance of the product.

SUMMARY OF THE INVENTION It is an object of this invention to provide apolymeric composition capable of attaining a high expansion whilemaintaining said technical merits in the case of using chemical agents.

It is another object of this invention to provide a polymericcomposition which gives in molding of crystalline polyolefins a shapedarticle devoid of sink mark and hollow portions and having a smooth flatsurface.

It is still another object of this invention to provide a polymericcomposition containing a chemical blowing agent capable of evolving alarge amount of gases.

The polymeric composition of this invention is characterized bycontaining as blowing agent a urea derivative of the formula:

ROCH: O H

wherein R is hydrogen or alkyl of l-5 carbon atoms and R is hydrogen or-CH OR EXPLANATION OF THE PREFERABLE EMBODIMENT We have unexpectedlyfound that the above mentioned drawbacks of the chemical blowing agentscan be overcome by using specific urea derivatives as blowing agent. Inaccordance with this invention, at least one of urea derivatives of theformula:

R 0 CH; O

I H /NJJN/ H R wherein R is hydrogen or a linear or branched chain alkylof l-S carbon atoms and R is hydrogen or -CH OR is used as blowingagent.

The urea derivatives used in this invention can be prepared byconventional method, i.e., by effecting addition of formaldehyde to ureato form methylolated urea and subsequent etherification undercondensation of the methylolated urea with an alcohol. A description ofurea derivatives appears in Beilsteins Handbuch der organischen Chemie,E III 3, pp. -114. In this case, the product is not an only compound,but often a mixture of urea, methylolated ureas and alkoxymethylatedureas. The use of such mixture also attains the objects of thisinvention.

The urea derivatives used in this invention include the followingcompounds: methylolated ureas such as monomethylolurea andN,N-dimethylolurea; and alkyl ethers of methylolated ureas such asmethoxymethylurea,

ethoxymethylurea,

n-butoxymethylurca,

isobutoxymethylurea, N-hydroxymethyl-N'-methoxymethylurea,N,N'-bis(methoxymethyl)urea, N-hydroxymethyl-N'-ethoxymethylurea,N,N'-bis(ethoxymethyl)urea, N,N'-bis(n-propoxymethyl)urea,

N,N'-bis (isopropoxymethyl) urea,N-hydroxymethyl-N'-n-butoxymethyl-urea, N,N'-bis (n-butoxymethyl urea,N,N-bis(sec-butoxymethyl)urea, N-hydroxymethyl-N'-isobutoxymethylurea,N,N'-bis isobutoxymethyl) urea, and N,N'-bis(pentyloxymethyl)urea.

Said urea derivatives are solid powders and are admixed with a polymericthermoplastic material to form a stable polymeric composition. When thepolymeric composition is heated at shaping temperatures above 100 C.,the urea derivatives undergo condensation accompanying liberation ofwater, alcohol or formaldehyde, the liberated water, alcohol orformaldehyde being vaporized b absorption of the latent heat ofevaporation whereby the polymer becomes cellular. Substances liberatedfrom a given amount of the urea derivative have a volume as vapor ofabout 500-700 ml./g. (calculated at C. and one atmosphere) and arecomposed predominantly of alcohols and water. The condensation reactionis endothermic and absorption of heat by the liberated substancespermits depression of the interfacial temperature of the polymer foamsand elevation of the viscosity of the foam surface, thus resulting instabilization of the foams and at the same time enabling a highexpansion. The urea-formaldehyde condensate formed by the condensationreaction is compatible with the polymeric thermoplastic material andimproves stiffness of the shaped polymeric article.

Alcohols liberated by said condensation reaction have to be vaporized atthe shaping temperature of polymer. For this reason, therefore, thenumber of carbon atoms in the alkyl group represented by R in theformula standing for the urea derivatives is limited to 1-5.

The polymeric composition of this invention may also containconventional additives such as heat stabilizers, UV-protecting agents,coloring agents, fillers, plasticizers, and the like. It is alsopossible to use jointl a small amount of ammonium chloride,triethanolamine or the like which can promote the condensation reactionof the urea derivatives.

The term polymeric thermoplastic material is intended to include anynormally solid polymer or mixture of polymers which is thermoplastic.Suitable polymers are vinyl polymers and include crystalline or rubberyolefin polymers such as polyethylene, polypropylene andethylene-propylene copolymer as well as polyvinyl chloride,polyvinylidene chloride, ethylene-vinyl acetate copolymer, polystyrene,acrylonitrile-butadiene-styrene terpolymer and ethylene-acrylic acidcopolymer.

In mixing of the polymer with the urea derivative, a master batchcontaining the urea derivative in a concentration higher than that foractual use is first prepared by way of a conventional dr mixing at atemperature low enough to inhibit foaming and then the master batch isworked up in a usual manner. It is also possible that the ureaderivative is dissolved or dispersed into a solvent such as water,methanol, ethanol or acetone and particles or powders of the polymer areimpregnated or mixed homogeneously with the resulting solution ordispersion.

The amount of the urea derivative employed will vary over a wide rangedependi g on t Sort Of the urea rivatives, shaping conditions such asshaping temperature, heating time and cooling time and the extent ofexpansion desired. In general the amount in terms of percent by weightbased on the polymeric composition is within 0.5- 20% when the expansionis more than 2, 01-10% when the expansion is 21.1 and '0.010.4% when theexpansion is less than 1.1 and inhibition of shrinkage of the shapedarticle is desired. A known exothermic chemical blowing agent such asazodicarbonamide may be used jointly with the composition of thisinvention providing the existence of such materials does not adverselyaffect the advantage of the invention. In such conjoint use, the foamsize of the resulting shaped article will be reduced as compared Withthe case of using the urea derivative singly.

Any of the conventional shaping techniques for polymeric thermoplasticmaterial, for example, injection, compression and extrusion, can beapplied to the polymeric composition of this invention to producemoldings and extrusions. The processing temperature varies according tothe sort of polymers and shaping methods but is usually selected fromthe range of l00270 C.

This invention will be explained more in detail by way of exampleswherein all of parts and percents are shown by weight unless otherwiseindicated.

Example 1 parts of powders of crystalline propylene-ethylene copolymerhaving a density of 0.91 g./ml. and a MFI (melt flow index; J'IS K6758,230 C.) of 3.2 were mixed with 1.0 part of N,N'-dimethylolurea. 2.0grams of the resultant mixture were placed in a test tube having aninside diameter of 15 mm., and previously heated for 30 minutes at C. inan oil bath, then heated at C. for 10 minutes. The mixture was thencooled in water at 20 C. to obtain a foamed product which was pure Whiteand had a uniform distribution of tine cells and an apparent density of0.37 g./ml.

Example 2 (a) The precedure of Example 1 was repeated except thatethylenevinyl acetate copolymer Elvax 250 (E. I. du Pont de Nemours &Co.) was used as polymer and the period of heating at 195 C. was 5minutes and 15 minutes. The resultant expanded products evidenced auniform distribution of fine cells, the apparent densities being 0.32g./ml. (5 minutes) and 0.33 g./ml. (15 minutes) respectively.

(b) For purposes of comparison, the procedure of Example 2(a) wasrepeated with the exception that n-heptane was employed as the blowingagent. An expanded product was obtained when the heating time at 195 C.was 5 minutes but only a shrunken and deformed product of an apparentdensity over 0.8 g./ml. resulted when the heating time at 195 C. was 15minutes. The reason why shrinkage of the expanded product was notobserved in Example 2(a) is understood to be ascribable to the fact thatwater which functions as blowing gas in this invention has a largecapacity of heat absorption.

Example 3 100 parts of granules of crystalline polypropylene having adensity of 0.91 g./ml. and MFI of 2.5 were mixed with 0.4 part ofN,N'-dimethylolurea. The resulting mixture was charged into a screw-linetype 5 oz. injection molding machine and injected into a mold (50 C.)under the following conditions: a cylinder temperature of 250 (3.,injection pressure of 1000 kg./cm. and injection time of about 5 sec.After 45 seconds, the moldings were taken out, the properties of whichare shown in Table 1.

The molding is in shape of a rectangular plate with two ribs. The baseplate is 40 mm., width, 135 mm., length, and the thickness thereof isvaried stepwise as 4 mm. in the range of 0 mm. to 45 mm. from one of theshorter side lines, 3 mm., in 45 mm. to 90 mm., and 2 mm. in 90 mmto 135mm. respectively.

Both of the ribs are the same rectangular plates having the dimensionsof length of 135 mm., thickness of 2 mm. and height of 5 mm. from thebottom of the base plate. One of the ribs is on one of the longer sidelines of the base plate and another is in the distance of 35 mm. from 6Such a high expansion of crystalline polyoleiins has never been obtainedby using a known conventional chemical blowing agent. When a shapingtreatment similar to that of this example was carried out using 2.0parts and 5.0 parts of 'azodicarbonamide, the expansion was 1.3 in

the other parallelling thereto. Most remarkable shrink-age 5 the formercase and 1.1 in the latter case wherein foams was observed in thecentral part (A) of the area where Were collapsed.

the thickness was altered from 4 mm. into 3 mm. and in Example 7 thecentral part (B) of the area where the thickness was l d f om 3 mm i 2mm 10 100 parts of crystalline propylene-ethylene copolymer Forcomparison, moldings were produced in a manner granules having a densityof gJml- Of a MFI 0f 26 similar to that of this example by using 0.3part of azodiwere mixed With (14 P of Y Y Y carbonamide ordinitrosopentamethylenetetramine conthoxyfilefllylohlfea by the aid ofall intensive mixer ventionally used as chemical blowing agent. Thepropern- The resulting mixture Was ihleeted into a ties of thesemoldings are also shown in Table 1. The 15 mo d in a ma er Similar tothat of Example 3 under foam diameter of the moldings shown in Table lwas the following conditions: a cylinder temperature of 260 within arange of 0.5 to 1 mm. 0., injection pressure of 1000 kg./cm. andinjection time TABLE 1 Comparative Examples Experiment number Blowingagent (part) Size of moldings (mm.):

Example 3 1 N,N-dimethylolurea (0.4)-.-.. Azodicarbonamide (0.3)---Dinitrosopentamethylenetetramine (0.3)-.-- None.

A area 3.75 3.76 3.73- 2.65. B area- 2.73" 2.74-- 2.53 2.23. Appear ceof moldings:

Shrinkage scarcely found Scareely found Scarcely found Remarkable.Surface.-- Smooth Smooth.

1 There were observed at least 10 small dimples having a diameter of0.2-2 mm. and a depth of about 0.1 mm.

Example 4 An injection molding operation was carried out similarly asdescribed in Example 3, using a composition which had been obtained bymixing 100 parts of granules of crystalline polypropylene having adensity of 0.91 g. /ml. and a MP1 of 2.5, 1.0 part of titanium dioxide(rutile type), 0.25 part of biurea and 0.05 part of N,N-dimethylolurea.The properties of the moldings are shown in Table 2. For comparison, theresuults obtained by using 0.3 part of biurea alone as blowing agent arealso shown in Table 2 as Comparative Example 4. Although both of themoldings had a fine foam of diameter at most 0.3 mm. and a smoothsurface, was less shrinkage was attained by the process of thisinvention.

A mixture of 100 parts of crystalline polypropylene powders having a MP1of 8.0 and 0.4 part of N,N'-dimethylolurea was charged into a mm.extruder maintained at a cylinder temperature of 170 C. and a dietemperature of 180 C. and extruded in the form of a round rod having adiameter of about 30 mm. White expanded moldings were thus obtainedwhich had an apparent density of 0.78 g./ml. and were composedsubstantially of closed foams. When 0.4 part of n-hexane was used forcomparison in place of N,N'-dimethylolurea, only poorly expanded moldinghaving an apparent density of 0.87 g./rnl. was obtained.

Example 6 100 parts of crystalline polypropylene powders having adensity of 0.91 g./ml. and a MFI of 6.0 were mixed with -a solution of2.0 parts of N,N-bis(methoxymethyl) urea dissolved in 5 .0 parts ofacetone. The resulting mixture was molded by extrusion at a cylinder of155 C. to form a white sheet having a thickness of about 4-5 mm. Theexpansion was 4 and the product was composed of almost closed foams.

of 2 seconds. After 45 seconds, the molded article was taken out, thesize of which was 3.78 mm. (A area) and 2.7-8 mm. (B area). Forcomparison, the size of the molded article obtained in the absence ofthe urea derivative was 2.64 mm. (A area) and 2.24 mm. (B area).

Example 8 parts of ethylene-propylene copolymer powders of a MFI of 8.1were mixed with a solution of 1.0 part of N,N-bis(isopropoxymethyl)ureadissolved in 5.0 parts of acetone. The resultant mixture was extruded ata cylinder temperature of C. The resultant expanded rod had an apparentdensity of 0.65 g./ml.

What is claimed is:

1. A polymeric composition comprising a polymeric thermoplastic resinselected from the group consisting of crystalline olefin homopolymersand copolymers of olefins, polystyrene and ethylene-vinyl acetatecopolymer admixed with a urea derivative in an amount within the rangeof 0.01 to 20 percent based on the weight of the polymeric thermoplasticresin, said urea derivative being at least one member selected from thegroup of compounds of the formula:

ROCH: O H

N -N/ H/ \R2 wherein R is hydrogen or alkyl of l-5 carbon atoms and R ishydrogen or CH OR 2. A process for the production of a cellularpolymeric thermoplastic body which comprises admixing a polymericthermoplastic resin selected from the group consisting of crystallineolefin homopolymers and copolymers of olefins, polystyrene andethylene-vinyl acetate copolymer with a urea derivative in an amountwithin the range of 0.01 to 20 percent based on the weight of thepolymeric thermoplastic resin, and heating the mixture to a temperaleastone member selected from the group of compounds of the formula R ocHl oH N E N wherein R is hydrogen or alkyl of 1-5 carbon atoms and R ishydrogen or CH OR 3. A composition according to claim 1 wherein the ureaderivative is monomethylolurea.

4. A composition according to claim 1 wherein the urea derivative isdimethylolurea.

5. A composition according to claim 1 wherein the urea derivative isN-hydroxymethyl-N'-methoxymethylurea.

6. A composition according to claim 1 wherein the urea derivative isN,N'-bis(methoxymethyl)urea.

7. A composition according to claim 1 wherein the urea derivative isN,N-bis(ethoxymethyl)urea.

8. A composition according to claim 1 wherein the urea derivative isN,N-bis(isoproporiymethyl)urea.

References Cited UNITED STATES PATENTS 2,403,465 7/1946 Pease 260-8542,410,395 10/ 1946 Smidth 260854 2,436,080 2/ 1948 Smith 2608542,376,653 5/1945 Boyer 260-2.5 F 2,016,199 lO/l935 HoWald 2602.5 F2,683,696 7/ 1954 Muller et a1. 260--2.5 D 3,547,839 12/1970 Tocker260-2.5 D 3,501,428 3/1970 Marans et a1 260-2.5 D 3,399,098 7/1968 Omotoet a1. 2602.5 E

MURRAY TILLMAN, Primary Examiner M. FOELAK, Assistant Examiner US. Cl.2602.5 HA, HB, 2.5 F, 2.5 P, 41 R, 41 B, 41.5 R

